Carbon Monoxide (CO) forms a covalent bond, consisting of one carbon atom and one oxygen atom. Understanding its chemical bonds helps explain its fundamental properties. This article clarifies why carbon monoxide is categorized as a covalent molecule.
The Fundamentals of Chemical Bonding
Chemical bonds are the forces that hold atoms together in molecules and compounds. Two types of chemical bonds are ionic and covalent. Ionic bonds form between a metal and a nonmetal, involving the complete transfer of valence electrons. The atom losing electrons becomes a positively charged ion (cation), while the atom gaining electrons becomes a negatively charged ion (anion); these oppositely charged ions attract each other.
Covalent bonds form between two nonmetal atoms through the sharing of electron pairs. This sharing allows each atom to achieve a stable electron configuration, often resembling that of a noble gas. The difference in electronegativity, an atom’s ability to attract electrons in a bond, determines the bond type. While pure ionic and pure covalent bonds represent two extremes, chemical bonding exists along a continuous spectrum.
Why Carbon Monoxide is Covalent
Carbon monoxide is a covalent compound because it is formed between two nonmetal atoms: carbon and oxygen. Both are located on the right side of the periodic table.
The carbon and oxygen atoms in carbon monoxide share electrons to achieve stable outer electron shells. They form a triple bond, consisting of one sigma (σ) bond and two pi (π) bonds. This sharing allows both atoms to satisfy the octet rule.
The electronegativity difference between carbon and oxygen further supports its classification as a covalent bond. Oxygen has a higher electronegativity (approximately 3.44) than carbon (approximately 2.55). However, this difference is not large enough for a complete electron transfer, which would create an ionic bond. Instead, electrons are shared, albeit unequally, leading to a covalent bond.
Understanding the Polarity of the CO Bond
Even within covalent bonds, electrons are not always shared equally between atoms. This unequal sharing occurs when one atom is more electronegative than the other, creating a “polar” covalent bond. The more electronegative atom pulls the shared electrons closer to itself, resulting in a partial negative charge on that atom and a partial positive charge on the less electronegative atom.
In the carbon monoxide molecule, oxygen is more electronegative than carbon. Consequently, the shared electrons are drawn more towards the oxygen atom. This uneven distribution of electron density creates a partial negative charge on the oxygen atom and a partial positive charge on the carbon atom.
This charge separation means the carbon monoxide bond is polar covalent. The unequal sharing of electrons and resulting partial charges give the CO molecule a small net dipole moment. This polarity is an important characteristic distinguishing it from nonpolar covalent bonds where electrons are shared equally.